Basque Country, Spain, late nineties. A young policewoman manages to infiltrate the ruthless terrorist gang ETA.
Ariadna discovers that her grandfather has been searching for the remains of his father, who disappeared during the Civil War. Determined to help him, she travels to Burgos, where a mass grave is being excavated, and where he could be buried. During her stay there, she will learn the story of Antoni Benaiges, a young teacher from Tarragona who was her grandfather's teacher before the war. Through an innovative pedagogical method, Antoni inspired his students and made them a promise: to take them to see the sea.